The ability to determine the location or position of a wireless device has become increasingly desirable as an ever increasing number of people carry wireless devices, such as mobile phones, pagers, wireless email/Internet devices, and communications radios on a daily basis. In most cases, because individuals carry the wireless devices on or about their person, it is a reasonable assumption that the position of a particular wireless device is also that of its owner. As a result, locating an individual may be accomplished by locating the wireless device they carry. The ability to locate individuals by determining the position of a wireless device has a variety of applications including search and rescue operations, and emergency situations.
Though consumer wireless devices generally have voice or data communication as a primary purpose, the signals emitted from such devices can be used to determine the location of the devices. The position can be determined by a number of methods including the known method shown in FIG. 12. The method shown by FIG. 12 determines the location of a wireless device 10 based on the time of arrival of a signal 11 at a series of antennas 12, 14, 16. The path length that the signal 11 travels to each antenna from wireless device 10 determines the time of arrival at each antenna. Based on the time of arrival, the distance between the wireless device 10 and each antenna 12, 14, 16 can be determined. Graphically, circles 13, 15, 17 surrounding each antenna 12, 14, 16 can be created based on the distance determined from the arrival time data. The intersection of these circles indicates the position of the wireless device 10. Alternatively, if the signal transmit time is unknown, time delay of arrival (TDOA) hyperbolic intersection can be used.
To make an accurate calculation of position, the time (delay) of arrival information must be accurately estimated. In complex environments, however, direct paths can be missing and multipath effects from reflection and scattering cause some signals traveling less direct paths to arrive at delayed times. As a result, the discrete arrival times of low bandwidth signals overlap and are smeared out over a period of time making calculation of position based on the arrival times difficult and inaccurate.
For example, known systems and methods have proved inadequate for locating wireless devices buried in the rubble of a collapsed building. The pervasive scattering and reflection from objects in the rubble interrupt the direct propagation path of a wireless device signal and introduce the multipath. These multipath effects make it difficult to determine the arrival time and direction of arrival, upon which known systems rely. As a result, known systems are unable to provide an accurate position of a wireless device buried in the rubble.
Therefore, what is needed are systems and methods for determining the position of a wireless device in a cluttered environment that do not suffer from the disadvantages of known approaches. Such systems would find many applications. In particular, in the example of the collapsed building rubble discussed above, the ability to locate a wireless device buried within the rubble would greatly assist in rescue efforts. Because of the likely proximity of a person to their wireless device, locating the wireless device would often yield the location of the person. Knowing the location of the person would allow recovery crews to focus excavation and recovery efforts on areas likely to have survivors.